1. Field of the Invention
The present invention relates to a catalyst for polyurethane having a delay property which is useful as a polyurethane foaming catalyst to be used for both flexible and rigid foams.
More particularly, the present invention relates to catalysts for polyurethane foaming having the delay property and which are prepared from an organic carboxylic acid salt of a tertiary amine and 1-methyl-4-(2-dimethylaminoethyl)piperazine. The polyurethane foam is manufactured by the reaction of organic polyisocyanate with a polyol which is carried out in the presence of a foaming agent, catalyst and other auxiliary agents. So far, a number of organic tin compounds and tertiary amine compounds have been known to be used as foaming catalysts for polyurethane and they have been frequently employed for industrial purposes either alone or in the form of a mixture.
2. Description of the Prior Art
Due to the remarkable progress of the polyurethane industry in recent years, polyurethane foams are produced in larger and more complicated forms. On the other hand, however, as short a time as possible is required from molding to demolding, to enhance the productivity of polyurethane foams. This type of demand is met by employing, as the starting polyol, high reactivity aminepolyols having a tertiary amine structure and modified polyols of high reactivity having primary OH groups at the end. The enhanced reactivity and the shortened molding time could be achieved by employing more active diphenylmethane-4,4'-diisocyanates, in place of toluenediisocyanate, and also by employing more active polyisocyanates containing the increased proportion of diphenylmethane-4,4'-diisocyanate, as organic polyisocyanate. When used in those highly reactive starting materials, the conventional polyurethane foaming catalysts such as organic tin compounds and tertiary amine compounds may introduce various problems. For example, when the conventional catalyst is used in highly reactive starting materials such as a mixture of an organic polyisocyanate and a polyol, the polymerization reaction occurs immediately, foams are produced vigorously, and the viscosity increases rapidly. Thus, the mixed liquid cannot be handled easily, cannot reach each corner of a large mold, and the foams produced flow poorly, and therefore some cavities remain in the large molds of complicated forms. In addition, polyurethane foams produced are liable to cause cracks and cleavages. If a low activity catalyst is used to avoid aforementioned disadvantages, the reaction proceeds slowly and the demolding time of the urethane foams is lengthened, leading to lowered productivity. For the purpose of preventing these disadvantages and enhancing the productivity, the development of catalysts having a so-called property has been sought for, which shows weak initial activity of a foaming catalyst for polyurethane and increasing activity as the foaming reaction proceeds.
Catalysts having the delay property are exemplified by the organic carboxylic acid salts of tertiary amines as described in Japanese Laid-Open Patent Application No. Sho 54-130697 and Japanese Patent Publication No. Sho 57-56491. The tertiary amine compound with organic carboxylic acids does not exhibit proper catalytic activity at the initial stage of the polyurethane forming reaction, because a total or part of the amino groups, depending on the circumstance, are blocked with the organic carboxylic acid. As the foam-producing reaction proceeds, however, the temperature is elevated, tertiary amines are dissociated thermally and, as a result, the catalytic activity inherent to the tertiary amine becomes exhibited. Known examples of the catalysts with this delay property are compounds of tertiary amines such as triethylenediamine and bis(2-dimethylaminoethyl)ether with organic carboxylic acids such as formic, cyanoacetic and 2-ethylhexanoic acids. However, these known catalysts having a delay property contain a large amount of organic carboxylic acids to suppress the initial activity of tertiary amine compounds. This fact results in a lower pH value, which may lead to disadvantageous corrosion of a catalyst tank and a foaming vessel. If, on the other hand, the disadvantage is lessened by applying a smaller amount of the organic acid, the pH can be increased but the delay property which is aimed at cannot occur.